The term “liquid” as used in the present description is understood as including viscous and non-viscous liquids as well as dispersions and fluid suspensions.
In particular, the invention relates to a machine for metering dyes and inks comprising a liquid phase and one or more solid pigments dispersed therein so as to form a homogeneous and stable product which, however, requires stirring and recirculation in order to maintain its homogeneity over time.
A problem in all the currently available machines, which generally have tanks exposed to the atmosphere, consists in the partial evaporation of the liquids and the deposition, on the bottom of the tank, of solid pigments. Such phenomena are responsible for significant variations in the flow characteristics of the product and variations in its colouring power (in the case of liquid dyes), resulting in a variation in the colouring capacity for the same metered amount used. Any variation in the colouring power which occurs with the tank full or nearly full, or in any intermediate filling situation, prevents or minimizes the possibility of obtaining over time identical tonalities of colour using the same quantity of dye.
In order to overcome this problem, during the reproduction of a given colour, the machines defined hereinbelow as belonging to Class 1 and 2 use a stirrer, but are not equipped with means for recirculation of the metered dyes; recirculation is envisaged only in much more costly apparatus which are defined below as belonging to Class 4.
The tinting machines for metering dyes for varnishes and paints, depending on their composition and performance characteristics, may be classified, by way of example, in four classes which are shown in the table below:
RECIRCU-LATIONTECH-TO TOPCLASSMETERINGNOLOGYOF TANKCOSTClass 1Manual meteringPlungerNo re-Mini-performed by meanscirculationmalof specially assignedstaff operating thepiston.Sequential meteringperformed by eachmetering circuit.Class 2Automatic meteringPlunger,No re-Lowperformed using abellows pump,circulationmotor driving anscrew pump,actuatinggear pumpmechanism.Sequential meteringperformed by eachmetering circuit.Class 3Automatic meteringPlunger,No re-Averageperformed using abellows pump,circulationmotor or anscrew pump,actuatinggear pumpmechanism.Simultaneousmetering performedby several meteringcircuits.Class 4Automatic meteringPlunger,The dyes areHighperformed using abellows pump,conveyed to themotor or anscrew pump,top of the tankactuatinggear pumpusing electri-mechanism.cally activatedSimultaneousvalvesmetering performedby several meteringcircuits.
The cost of production of these machines increases exponentially from Class 1 to Class 4.The machines with plunger pump, bellows pump or cavitation pumps, belonging to Class 2, represent approximately 70 to 80% of the world market, owing to their low production cost and consequently low sales price. All these machines do not have a circuit for recirculation of the dyes to the top of the tank. A machine belonging to Class 2 comprises, for each colouring agent to be metered, a tank communicating with a plunger pump, bellows pump or cavitation pump or other pumping means suitable for removing the dyes from the tank, manually or by means of a suitable drive system. An electronic control and operating unit, with associated software, may be provided for selecting and metering the required dyes and the metered quantity. In automatic tinting machines which belong to Class 4 and which use volumetric gear pumps, piston pumps or other pumping means and which are operated by a single motor or by multiple motors, the dyes are recirculated from the bottom of the tank to the top of the tank by means of a two-way or three-way solenoid valve, for each dye metering circuit. In this case, the consistency in reproduction of the colour tonality is very high, but these machines have, by way of a major drawback, a high production cost and high cost of spare parts, with the need for very expensive additional electrical/electronic components.